1. Field of the Invention
The present invention relates to a photosensitive printing plate. More particularly, the present invention relates to a photosensitive printing plate in which an o-quinonediazide is used.
2. Description of the Prior Art
In general, photosensitive printing plates are classified into planographic plates, intaglio plates, and relief plates. A photosensitive planographic printing plate is produced by rendering the surface of a support hydrophilic by chemically or physically treating the surface or by coating a hydrophilic polymer material on the surface, and then coating the following photosensitive materials on the thus prepared hydrophilic surface. Photosensitive materials for negative working as used in a photosensitive planographic printing plates are a p-diazodiphenylamine-formaldehyde condensation product as described in German Patent No. 596,731 and derivatives thereof, 3-nitroanthranilic acid as described in U.S. Pat. No. 2,729,562, diazo derivatives of aromatic or heterocyclic amines as described in German Pat. No. 949,383, a reaction product of a diazosulfonic acid salt and a diazonium salt as described in U.S. Pat. No. 2,890,115, an acrylic acid ester of pentaerythritol as described in Japanese Patent Publication No. 3271/1971, polyvinyl cinnamate as described in U.S. Pat. No. 3,357,831, and the like; and photosensitive materials for positive working are o-naphthoquinone diazide derivatives as described in Liebig, Ann. Chem., 598,123, (1956), a reaction product of potassium ferrocyanide and p-diazodiphenylamine as described in U.S. Pat. No. 3,113,023, a reaction product of a heteropoly-acid or an isopoly-acid selected from groups Va and VIa of the Periodic Table and a diazonium salt as described in Japanese Patent Publication No. 7663/1964, diazo and a polymer coupler as described in U.S. Pat. No. 2,687,958, tetraallyl borate as described in Phot. Sci. Eng., 16 (4), 300-312, and the like.
Hitherto, as materials for negative working, compounds containing a diazonium salt as a major component have been mainly used. Recently, the development of a presensitized (PS) plate of high printing durability utilizing a photo-cross linking or photo polymerization reaction has been extensively conducted, and some plates have been used practically.
On the other hand, for positive working, ink receptive compounds are used which are changeable into compounds, which can be developed in alcohol or a weak base, by light transformation or light decomposition. Most of the practically used compounds are o-quinonediazido compounds such as o-quinonediazido sulfonyl esters or acid amides, and the like. These compound are changed into 5-membered cyclic carboxylic acids by light irradiation, and the exposed areas are dissolved and removed by developing with an alkaline solution. Thus, a positive image is obtained using a positive original image. This method is described in U.S. Pat. Nos. 3,046,121 and 3,046,122. In addition, various quinonediazide type compounds have been reported. Most of these compounds are low molecular weight compounds, and are crystalline when used alone. As a result, the mechanical strength of the layer is low and it is difficult to print a large number of sheets.
Hence, alcohol soluble resins such as a phenolformaldehyde resin, a styrene-maleic anhydride resin, shellac, and the like are used as a binder to prevent the crystal-separation of the photosensitive layer and, at the same time, to improve the mechanical strength of the image obtained. However, there are less of these types of plates having sufficiently satisfactory printing durability as compared with the above described negative type plates.
In order to increase the printing durability, an operation called "burning in" is conducted after exposure and development. In this operation, it is generally necessary to heat the plate at 180.degree. C. for 30 to 40 minutes, and, at this time, considerable care must be taken not to form temperature-unevenness on the surface of the plate. However, the operation is conducted by a plate maker who uses the photosensitive printing plate, and thus, the printing durability, as a matter of fact, varies depending upon the skill of the plate maker.